This invention relates in general to vehicle disc brake assemblies and in particular to an improved structure for a bleeder screw adapted for use in such a vehicle disc brake assembly.
Most vehicles are equipped with a brake system for retarding or stopping movement of the vehicle in a controlled manner. A typical brake system for an automobile and light duty truck includes a disc brake assembly for the front wheels of the vehicle, and either a disc brake assembly or a drum brake assembly for the rear wheels of the vehicle. A typical brake system for a medium duty truck includes a disc brake assembly on all four wheels of the vehicle. The brake assemblies are typically actuated by hydraulic or pneumatic pressure generated when an operator of the vehicle depresses a brake pedal. The structures of the disc brake assembly, as well as the actuators therefor, are well known in the art.
There are two basic types of calipers for use in disc brake assemblies, namely, a "floating" caliper disc brake assembly, and a "fixed" caliper disc brake assembly. A floating caliper type of disc brake assembly is usually used on automobiles and light and medium duty trucks. A conventional floating caliper type of disc brake assembly includes a brake caliper which is supported by a pair of pins for sliding movement relative to an anchor plate which is secured to a fixed, non-rotatable component of the vehicle. A fixed caliper type of disc brake assembly is sometimes used on automobiles and light and medium duty trucks. A conventional fixed caliper type of disc brake assembly includes a brake caliper which is solidly fixed to a fixed, non-rotatable component of the vehicle.
In both types of disc brake assemblies, a pair of brake shoes are supported by the disc brake assembly for sliding movement relative thereto. The brake shoes have respective friction pads which are disposed on opposite sides of a rotor. The rotor, in turn, is connected to the wheel of the vehicle for rotation therewith. To effect braking action, the brake shoes are moved inwardly toward one another so as to frictionally engage the opposed sides of the rotor. Such frictional engagement causes retarding or stopping of the rotational movement of the rotor and, therefore, the wheel of the vehicle in a controlled manner.
To accomplish this in a fixed caliper type of disc brake assembly, the brake caliper assembly includes an inboard caliper assembly disposed adjacent an inboard brake shoe and an outboard caliper assembly disposed adjacent an outboard brake shoe. One or more hydraulically or pneumatically actuated pistons are provided in respective cylindrical recesses formed in the inboard caliper assembly adjacent the inboard brake shoe, and one or more hydraulic, ally or pneumatically actuated; pistons are provided in respective cylindrical recesses formed in the outboard caliper assembly adjacent the outboard brake shoe. This type of construction is commonly referred to as an "opposed" piston caliper design. When the brake pedal is depressed, the pistons urge the brake shoes toward one another and into engagement with the associated side of the rotor. As result, the brake shoes frictionally engage the opposed sides of the rotor.
Typically, when the disc brake assembly is initially connected to the vehicle hydraulic or pneumatic brake system, air is present in the system. Thus, the disc brake assembly includes one or more bleeder screws which are used to bleed the air from the vehicle brake system. The bleeder screw is secured in a threaded aperture provided in the disc brake assembly and is connected via a passageway to the associated fluid chamber thereof. A typical bleeder screw includes a passageway formed therethrough to bleed the air from the brake system. The bleeder screw typically remains secured to the disc brake assembly and, when not being used, includes a cap installed on the outer end thereof.
In order to bleed air from the brake system, the cap is removed and the bleeder screw is slightly unscrewed to allow the air to escape through the passageway to the atmosphere in a known manner. Unfortunately, once the disc brake assembly is installed on the vehicle, the disc brake assembly is subject to dirt, mud, water, and other debris which may damage and corrode the threads of the bleeder screw and aperture. Thus, when it is attempted to unscrew the bleeder screw, the bleeder screw may become seized in the aperture and/or brake during this process. In order to prevent this, it is known to coat the threads of the bleeder screw, the threads of the aperture, or both with a corrosion resistant coating. However, the: coating is subject to chipping, wear, and related deterioration. Also, in a hydraulically actuated disc brake system, the corrosion from the threads may become dispersed in the hydraulic brake fluid and affect the operation of the system. Thus, it would be desirable to provide an improved structure for a brake bleeder screw for use in a disc brake assembly which protects the threads of the bleeder screw and aperture of the disc brake assembly, yet is relatively inexpensive and easy to manufacture.